The present invention relates to a glass melting plant, in particular for the production of fiberglass, having a melt crucible, raw materials being supplied to the melt crucible by a supply device, and melted there.
Glass melting plants can be heated by submerged combustion heaters. The advantage of such a glass melting plant is that a high melting performance is achieved in a small space.
Such a glass melting plant has already been described in U.S. Pat. No. 3,260,587. This glass melting plant has a melt chamber having submerged combustion heaters into which the raw material is delivered via a supply device. The submerged combustion heaters are situated completely within the liquid glass. Connected to the outlet of the melt chamber is a refiner segment, and a weir (raised part) extends over the entire width of the melt chamber in the area of the outlet.
In such melting plants having submerged combustion heaters, the problem frequently arises that the glass melt contains a high portion of gas bubbles. Here there is the theory that the bubble content arises from a reaction of the fossil fuel and the oxidant of the submerged combustion heater. The exothermic reaction of the two gaseous materials takes place inside the glass melt, and as reaction product from the fuel and the oxidant (as a rule, oxygen) there result carbon dioxide and water vapor. These reaction products form fine bubbles having a diameter of from 0.1 mm to 1 mm, and the bubbles reduce the quality of the glass melt. A gas portion in the glass melt of up to 30 vol. % has been reported.
In the use of conventional melting technology, depending on the product, the requirement with regard to bubble content is described by the measurement quantity number of bubbles per weight of the sample. Required quality levels of the glass product are between 0.1 bubble/1000 g glass and 100 bubbles/100 g glass. Frequently, the size of the bubbles also has to be within a specified range. In glass melting plants that are heated by submerged combustion heaters, such quality requirements often cannot be met. Therefore, this melting technology is frequently limited to the production of fiberglass, or glass and stone wool. These products are used for the production of insulating mats in which the bubble content of the fibers does not have a disadvantageous effect.
In order to make it possible to use the melting technology that is advantageous with regard to space requirements and melting performance for further applications as well, or to increase the quality of the produced glass, it is desirable to reduce the bubble content of the glass melt. For this purpose, in the glass melting plant known from U.S. Pat. No. 3,606,825, a refiner zone is provided in order to remove or release bubbles or other gaseous inclusions from the glass melt. The glass melting plant having submerged combustion heaters described in US 2004/0224833 A1 also has a refiner region connected to the glass melting tank. The glass melt heated by the submerged combustion heaters is, however, produced only in a side stream, and is supplied to the main stream glass melt, in particular, in the area of a feeder that is provided with mechanical homogenizing units for mixing the glass flowing out from the main stream and flowing together in the side stream.
In order to reduce the portion of foam or bubbles in the glass melt, US 2015/0197440 A1 proposes that, in a tank following the melt crucible, and having a floor, a roof, and a side wall structure that connects the floor and the roof, the glass melt permeated with the foam and bubbles be heated in order to maintain or raise the temperature of the glass melt and in addition to control the composition of the gas above the glass melt in the tank, e.g., its water saturation, and/or to agitate the surface of the glass melt using a liquid or solid composition, for example, using drops of water.
In US 2009/0235695 A1, in contrast, for the homogenization of the glass melt it is proposed to provide, in the glass melt tank above a submerged combustion heater, a burner situated in the superstructure whose flame in the region of the glass melt impinges on the surface of the melt, in which region the bubbles produced by the submerged combustion heater reach the surface of the glass melt.
A glass melting plant having a refining region for the reduction of the portion of bubbles is also described in U.S. Pat. No. 8,402,787 B2, where a movable refiner tank has at its input a shaft that is made such that the transfer of the molten glass to the refiner region takes place with a minimal loss of heat.
In US 2015/0315057, it is further proposed, for the removal of foam and bubbles from the glass melt, to use acoustic waves or particle radiation, for example, using compounds containing sulfur, glass shards, ground glass, particles having a composition that can be integrated into the molten glass, frozen CO2, solid organic materials, or combinations or mixtures thereof. In addition, it is proposed to remove the foam or the bubbles through continuous or intermittent agitation with material woven in the manner of a sieve, or non-woven material.
The solutions described above are however complex and cost-intensive, or change the composition of the glass melt. In addition, the desired improvement of quality is frequently still not achieved.